Metro Detroit weather: First blast of winter next week

More changes ahead

By Paul Gross - Meteorologist
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DETROIT - The pattern change back to more typical early winter temperatures occurred right on schedule, and we’ve been mired in the upper 30s to near 40 degrees (4 degrees Celsius for our Canadian friends) Thursday afternoon, with wind chills down in the low 30s (0 degrees Celsius).

Some of us even started the day with a few wet snowflakes, but with above freezing temperatures, none of the snow actually stuck once it hit the ground. If Thursday was a shock to you, wait until you see what’s coming our way next week.

Thursday night will be mostly cloudy, and any scattered early evening light rain showers should gradually taper off. Lows will be in the mid-30s (1-2 degrees Celsius). West-southwest winds will blow at 10-15 mph.

It will be mostly cloudy on Friday, and it’ll still be breezy. Highs will once again only near 40 degrees (4-5 degrees Celsius). West winds will blow at 10-20 mph.

Friday’s sunrise is at 7:44 a.m., and Friday’s sunset is at 5:02 p.m.

Friday night will be mostly cloudy, with lows near 30 degrees (minus 1 degree Celsius).

It will be mostly cloudy on Saturday, with highs near 40 degrees (4-5 degrees Celsius).

Saturday night will be mostly cloudy, with lows in the upper 20s (minus 1 to minus 2 degrees Celsius).

Sunday is still a very intriguing day. An upper-level system will cross the Great Lakes during the afternoon and evening, pushing moisture out ahead of it. That moisture will fall as something -- either rain or snow.

There are some important differences among my computer models in terms of how much low-level warmth we’ll have, but right now, I’m leaning toward a slightly cooler solution to this question. The upshot is that we’ll probably have some wet snow develop sometime Sunday afternoon.

Above-freezing highs in the upper 30s (4 degrees Celsius) will ensure that nothing sticks to paved surfaces. But as temperatures drop in the evening, it’s possible that we’ll see elevated surfaces (decks, mailboxes, blades of grass) pick up a dusting.

Keep in mind that this could end up as a snow-in-the-north, rain-in-the-south situation, depending on which model verifies. I should have a much better handle on this by Friday, so come back and I’ll share my latest thoughts. Don’t forget to follow me on Twitter @PGLocal4 and @Local4Casters, as I will tweet important updates if there are any changes over the weekend.

Monday should be a quiet weather day, with mostly cloudy skies, and highs in the mid-40s (6-7 degrees Celsius).

Rain will develop Tuesday, with highs in the mid- to upper 40s (8-9 degrees Celsius).

Wednesday is where things get really difficult from a forecast standpoint. You might recall my discussion Monday about a storm and the Arctic Blast that will follow. The long-range computer models are still having great difficulties with the timing and strength of this system.

I am copying below two of the models, centered on 7 p.m. Wednesday. There are two things to notice on the maps: the black lines (surface pressure lines), and the colored bands (a parameter analogous to temperature).

Notice how the ECMWF has a weak surface low pressure (the little black circle) over northern Lake Michigan, with the much colder air (the darker blues) back to our west. Then take a look at the GFS: the surface low is a powerful one that’s much farther north and east (and the closer the black pressure lines are together, the windier it is), and also how much farther east the cold air has progressed.

There are significant ramifications to these differences. If we take the ECMWF at face value, Wednesday will have some rain showers, milder temperatures and the cold blast not arriving until Thursday. If we take the GFS at face value, Wednesday will be extremely windy with sharply falling temperatures and lake effect snow bands developing.

There’s another monkey-wrench thrown in that will help you appreciate how difficult these forecast can be for meteorologists. Wednesday, the ECMWF didn’t agree with the other models (it brought the big storm through much faster), while the GFS was consistent with a slower-moving storm. Thursday's GFS has reversed itself and has now sped up the storm considerably. These big day-to-day changes in how the models handle a system are also reason for pause.

Regardless of the timing, our first sharp blast of winter weather will be here next Thursday and Friday, with highs in the low to mid-30s (minus 1 to 0 degrees Celsius), and strong wind obviously making it feel much colder. If a consistent, strong west wind develops, some lake effect bands will develop.

This could be our first accumulating snow for some, but the exact wind direction will dictate this. I won’t be able to get specific until early next week.

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